Automatic electric drip coffee makers produced commercially for the household appliance market, and others, are of two basic configurations. In one configuration the heating elements are attached to the beverage storage container so that they are inseparable by the user, as with percolators and devices as described in my prior patent. In the more conventional configuration the beverage storage container is not itself electrified, but rests instead on an electrically heated hot plate or the like. Either configuration may employ gravity to continuously transport heated water to the coffee bed below a water reservoir, or may employ a lifting system such as the well-known percolator pump arrangement to incrementally transport heated water to the coffee bed located above a water reservoir.
My prior patent discloses a drip type coffee maker which uses a percolator type pump to lift hot water increments to a basket of coffee grounds, as well as one that depends on gravity flow. The device is constructed so that only water passes to the coffee bed, and the resulting brewed coffee is collected and maintained in a beverage storage container which is separate from the water applied to the coffee bed. Thus the brewed coffee does not enter the pump well to be vigorously boiled and re-boiled in the pump well, and the known bitterness imparted by such action is avoided. In the device described in my prior patent, and in the more conventional configuration, the total volume of water and the volume of coffee beverage ultimately brewed must be contained within separate chambers forming part of the overall device. Thus both compartments must be of a size sufficient to hold a volume of liquid equivalent to the full amount required to brew the desired volume of coffee beverage. Therefore, if for example, a 10 cup percolator were to be converted to a drip process unit, using the concept of my prior patent and yet still retain the 10 cup capacity, then the water reservoir and coffee basket would have to be located largely outside the percolator body, thereby greatly increasing the total volume of the device. Alternatively, if the water reservoir is placed wholly within the existing percolator container to achieve a manageable size, then the coffee brewing capacity of the device would be severely reduced, i.e., approximately 50%. The more conventionally configured drip coffee makers are similarly handicapped by requiring both the beverage storage container and the water reservoir to each be capable of holding the total quantity of liquid employed.
Furthermore, the coffee makers described in my prior patent, and electric percolators, and electric household drip coffee makers in general, simultaneously heat and brew, by incrementally or continuously transporting heated solvent (water in the case of drip coffee makers; water followed by re-cycled beverage in the case of percolators) to the coffee bed while some portion of the remainder is being heated. Given the typical fixed wattage coffee maker with a convenient, low cost, fixed dimension coffee basket, the strength or percent dissolved solids of the resulting beverage will increase with an increase in cups brewed for the following reasons: one, a greater quantity of solvent is provided to the coffee bed over a greater period of time as cups brewed increases, and two, each increment of solvent takes longer to pass through the coffee bed, since the depth of the coffee bed increases as cups brewed increases. Solids extraction is in turn proportional to the amount of water contacting a specific quantity of grounds in a given length of time, and to the length of time a given quantity of water is in contact with the grounds.
User-operated mechanism to: (a) decrease the cross sectional area of the coffee basket as quantity brewed decreases (tending to maintain a fixed depth of grounds) or, (b), to vary the amount of heated solvent which is diverted around rather than through the coffee bed in inverse relation to quantity brewed, are mechanisms sometimes employed to compensate for these effects. The penalties are increased complexity, with attendant increase in economic cost and increased difficulty in cleaning by the housewife or other user.